The invention relates to a device for controlling the primary drive of a hydraulically driven fine blanking press, comprising a main cylinder, which is disposed in the base and in which the main piston/ram is guided, which can be acted on by hydraulic fluid via pressure chambers, carries out a stroke movement between BDC and TDC in the direction of the stroke axis and supports a table, further comprising double-acting fast stroke pistons, which are guided in fast stroke cylinders, can be acted on by hydraulic fluid via pressure chambers, and include piston rods for the rapid approach/probe stroke of the main piston and the table plate, and a hydraulic system, which includes at least one hydraulic pump unit, for supplying the pressure chambers with the hydraulic fluid that is set by a central control unit to a predefined working pressure.
The invention further relates to a method for controlling the primary drive of a hydraulically driven fine blanking press, comprising a main piston, which is guided in a main cylinder of the base, supports a table, and carries out a stroke movement between the lower dead point UT and and the upper dead point OT, in which the main piston, together with the table, is displaced in the rapid approach/probe stroke between UT and OT, or OT and UT, by pressurization of the pressure chambers of a fast stroke piston disposed in the fast stroke cylinder, the rapid motion/probe stroke is then ended, and subsequently the main piston, during the power stroke, carries out the blanking or forming operation, wherein the pressure chambers of the main piston are acted on by a working pressure of a hydraulic fluid from a hydraulic system which is predefined by a central control unit and generated by a hydraulic pump unit.
The fine blanking process requires specific triple-action presses, which essentially operate from the bottom to the top and enable a controlled regulation of the blanking operation, including the auxiliary functions for the vee ring, pressure pad and ejector. The vee ring force and the counter force are generated hydraulically, and the blanking force is generated mechanically or hydraulically.
A number of piston arrangements exist, which are used in presses for driving or pressurization purposes. The prior art according to DE 2 218 476 A1 and DE 2 264 429 A1 relates to a fine blanking press comprising two rigidly connected frame parts, on which two table bodies are arranged, which are used to clamp on two tool parts and which can be displaced by hydraulic means axially toward and away from each other. A cylindrical chamber is provided in the first frame part and receives therein two pistons movable coaxially relative to each other, with the first piston being connected to a piston rod and the second surrounding this piston rod and forming part of the first table body arranged displaceably on the first frame part. The second piston has a female thread and is screwed to a bushing having a male thread, so that the axial position of the second piston can be set.
From DE 195 24 042, a method for regulating the drive is known, in particular for a hydraulic press for forming and/or cutting metal sheets, comprising at least one double-acting piston-cylinder unit for driving a press ram. This press operates in the direction of gravity, which is to say from top to bottom. During a first working phase of the press, the top and bottom cylinder chambers of the piston-cylinder unit are connected via a valve system during the downward motion of the unloaded press ram. A motor/pump system comprising a volume-controlled hydraulic motor/pump system is provided for the subsequent forming phase, the system being driven at least via a chargeable accumulator system, and the regulatable torque can be supplied to a regulatable pump system.
DE 198 22 436 A1 describes a method for operating a hydraulic press, in which the force required for deforming a workpiece is created by the piston of a double-acting cylinder, and this force is transmitted via mechanical intermediate members from the piston to a press tool, wherein the press tool impinges on the workpiece only after the press tool has traversed a first length of travel, and forming then takes place while a second length of travel is being traversed. The press operates from top to bottom, and the rapid approach is essentially caused by the inherent weight of the press crosshead when the pressure is relieved.
DE 10 2012 006 981 A1 discloses a hydraulic press comprising a ram, which can be adjusted by way of a hydraulic drive device, wherein the hydraulic drive device comprises a working cylinder in which a drive piston is displaceably received, which divides the interior of the drive cylinder into a first working chamber and a second working chamber, which can be acted on by a hydraulic fluid. At least one hydraulic return device is provided so as to bring the ram into the starting position thereof after the forming process.
The basic idea of this known prior art is to discharge the hydraulic fluid during the forming process from the second working chamber via a pump into the storage tank.
Providing rapid approach cylinders during the advance stroke of the press ram are known from a number of solutions (DE 196 43 635 A1, DE 197 41 879 A1, DE 198 22 436 A1, DE 102 15 003 A1, DE 10 2004 006 126 B4, DE 10 2009 058 407 A1, EP 0 311 779 B1, EP 0 615 837 B1, EP 891 235 B1.)
In all these known solutions, the main piston and the rapid approach piston belong to separate hydraulic circuits, in which the hydraulic fluid displaced from the working chambers is either discharged during the downward motion of the pistons into a tank ((DE 10 2009 058 407A1), or shifted from the top working chamber into the bottom working chamber (DE 10 2004 006 126 B4, DE 196 42 635 A1, DE 102 15 003 A1, EP 0 891 235 B1).
This shifting is carried out in separately routed hydraulic tubes, and independently of the position of the fast stroke piston in the fast stroke cylinder. The fast stroke cylinders are generally disposed on the head piece of the press and must therefore be able to support the entire top structure of the press, including the traverse member, and lift it during the advance stroke. The primary drive/ram of these known presses is not equipped with a rapid approach function or fast stroke cylinder, so that the cycle time or the achievable number of strokes is accordingly low.